Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$121.44	7.443%	$130.4788	$130.48	$130.50	$130.50
Purchase #2	$125.27	4.796%	$131.2779	$131.28	$131.30	$131.30
Purchase #3	$141.54	6.771%	$151.1237	$151.12	$151.10	$151.10
Purchase #4	$102.79	11.465%	$114.5749	$114.57	$114.55	$114.60
Purchase #5	$49.88	5.340%	$52.5436	$52.54	$52.55	$52.50
Purchase #6	$51.97	7.704%	$55.9738	$55.97	$55.95	$56.00
Purchase #7	$135.99	4.846%	$142.5801	$142.58	$142.60	$142.60
7 purchase totals =	$728.88		$778.5528	$778.54	$778.55	$778.60